Starting a business is about seeing a problem, solution, and/or opportunity, and being able to execute it with domain expertise, all at the right time. Of course, it's also about grinding out sales leads and finding paying customers – a lot of is is sinking way more hours into it than you would sink into a 9 to 5.
I don't think this process is successful very often when we use the "daydreaming" method encompassed in the way your question is phrased here.
There aren't a lot of ways to "quit my job real quick." Most businesses are going to involve way more work than a day job, and the ideas can't just come out of thin air or from strangers on the Internet. Frankly, my advice to someone daydreaming is to just look around for more fulfilling salaried work.